1. Field of the Invention
The present invention relates to a rectangular-shaped deflection yoke, RTC (Round Core Tetra Coil Combined Deflection Yoke) for enhancing deflection sensitivity of a color cathode-ray tube. More specifically, the present invention relates to a deflection yoke structure for a color cathode-ray tube that is mounted with rectangular shaped deflection coils and a circular shaped ferrite core, and a gap therebetween is not uniform. Rather, the difference between a maximum gap and a minimum gap is greatest at an end section on a screen side of the ferrite core.
2. Background of the Related Art
As depicted in FIG. 1, a color cathode-ray tube includes a panel 1 mounted in a front surface of the cathode-ray tube, a fluorescent screen 3 placed on an inner surface of the panel 1, three primary colors (chrominance signals), namely R, G, and B, are being applied to the screen, a shadow mask 2 for selecting a color incidented on the fluorescent screen 3, a funnel 6 coupled to a rear surface of the panel 1 for maintaining the inside of the tube in a vacuum state, electron guns 5 mounted inside of a tube-shaped neck portion on the rear side of the funnel 6 for emitting electron beams, and a deflection yoke 4 that surrounds an outside of the funnel 6 and deflects the electron beams in the horizontal and vertical directions.
A generally known color cathode-ray tube uses a three-beam in-line type electron gun. In such a cathode-ray tube, R, G, and B electron beams are arranged in parallel, and a self-converging principle using non-homogenous (non-uniform) magnetic fields is applied thereto for converging those three electron beams on one point of the fluorescent screen 3.
Particularly, the deflection yoke 4, as illustrated in FIGS. 2a and 2b, includes a pair of horizontal deflection coils 41 for deflecting electron beams emitted from the electron guns 5 in the horizontal direction, a pair of vertical deflection coils for deflecting electron beams emitted from the electron guns 5 in the vertical direction, a ferrite core 44 for enhancing a magnetic efficiency by minimizing a loss in a magnetic force generated by the horizontal and vertical deflection coils, a holder 43 for fixing the horizontal and vertical deflection coils and the ferrite core at predetermined positions and insulating the horizontal and vertical deflection coils, a COMA free coil 45 mounted in a neck portion of the holder 43 for improving comma aberration caused by a vertical barrel type magnetic field, a ring band 46 mounted in an end of the neck portion of the holder 43 for mechanically coupling the cathode-ray tube with the deflection yoke 4, and a magnet 47 mounted in an end of an aperture side of the deflection yoke 4 for correcting raster distortion (hereinafter, it is referred to as distortion).
Thusly constituted deflection yoke 4 can be divided into several kinds, as shown in Table 1, in accordance with a sectional configuration of an end portion of the screen side of the horizontal, vertical deflection coils 41,42 and the ferrite core 44.
That is, as depicted in FIGS. 4 and 5, if the horizontal and vertical deflection coils 41, 42 have a circular shape, the sectional configuration of the end portion of the screen side of the ferrite core 44 is also circular. Similarly, if the horizontal and vertical deflection coils 41, 42 have a rectangular shape, the sectional configuration of the end portion of the screen side of the ferrite core 44 is also rectangular.
TABLE 1HorizontalVerticalDeflectiondeflectiondeflectionFerrite coreyokecoilcoilCircular deflectionCircularCircularCircular coreyokecoilcoilRAC deflectionRectangularRectangularRectangular coreyokecoilcoil
Especially, the RAC deflection yoke 4 has a more improved deflection sensitivity than the circular deflection yoke 4 because the sectional configuration of the end portion of the screen side for the horizontal and vertical deflection coils 41, 42 and the ferrite core 44 in the RAC deflection yoke 4 is a rectangular shape, respectively, and thus can shorten the distance between electron beams.
In general, the conventional deflection yoke 4 allows a current having a frequency of 15.75 KHz or above to travel in the horizontal deflection coil 41, and using the magnetic field generated around the coil, deflects electron beams inside of the cathode ray tube in the horizontal direction. Also, the conventional deflection yoke 4 allows a current having a frequency of 60 Hz to travel in the vertical deflection coil 42, and using the magnetic field generated around the coil, deflects electron beams inside of the cathode ray tube in the vertical direction.
One of recently developed deflection yokes is a self-convergence type deflection yoke 4, which uses the non-uniform magnetic fields around the horizontal and vertical deflection coils 41, 42 in order to converge three electron beams on a screen, without using a separate additional circuit or device.
In other words, by adjusting the winding distribution of the horizontal and vertical deflection coils 41, 42, the self-convergence type deflection yoke 4 creates a barrel or pin-cushion shaped magnetic field for each section (i.e., aperture section, middle section, neck section), and allows three electron beams to experience a different deflecting force from one another depending on their positions, yet to converge upon one point from different distances although each electron beam starts and ends in different positions from one another.
Meanwhile, when an attempt was made to generate a magnetic field by providing a current to the deflection coil, it was discovered that it was not an easy task to deflect electron beams to the entire surface of the screen using only the magnetic field generated by the coil. To avoid such difficulties, many now use the ferrite core 44 having a high permeability, hoping to minimize any loss in the magnetic field on its way of return and consequently to enhance the magnetic efficiency and magnetic force.
Referring to FIG. 7, each of the pair of horizontal deflection coil consists of a rectangular-shaped upper horizontal deflection coil and a rectangular-shaped lower horizontal deflection coil. The pin-cushion shaped horizontal deflection magnetic field is created by connecting the upper and lower horizontal deflection coils in parallel as illustrated in FIG. 3a, and allowing a saw-tooth shaped horizontally deflecting current to travel in the coils (see FIG. 3b).
The deflection yoke with the constitution described above can be largely divided into two groups.
One of them is associated with the circular deflection yoke 4 where the horizontal and vertical deflection coils 41, 42 have a circular shape, and the sectional configuration of the end portion of the screen side is also circular as shown in FIGS. 4 and 5. In such case, the area ratio of an aperture section of the neck side of the deflection coil to an aperture section on the screen side of the deflection coil is not smaller than 10 to 1, meaning that the center of the deflection slants toward the neck side.
In reality, though, the position of the deflection yoke mounted in the cathode ray tube should be designed in such a manner that it inclines to the screen side, not the neck side, in order to reserve a little allowance against BSN (Beam Strike Neck) phenomenon, namely electron beams emitted from the electron guns strike the inner surface of the funnel. This unfortunately weakens the deflection sensitivity a great deal.
The other is associated with the RAC type deflection yoke 4 where the configuration of the horizontal and vertical deflection coils 41, 42 and the ferrite core 44 are all rectangular. As depicted in FIGS. 6 and 7, three electron beams emitted from the electron guns 5, namely red, green, and blue beams, pass through the horizontally deflected magnetic field, and according to the Fleming's left hand rule the electron beams are deflected in the horizontal direction, being inversely proportional to the cube of the distance between the inner surface of the horizontal deflection coil and the electron beams.
Therefore, if the horizontal and vertical deflection coils 41, 42 have a rectangular shape, the distance between the electron beams and the deflection coil becomes shorter by 20% and the horizontal and vertical deflection sensitivities can be improved up to approximately 20˜30%.
To summarize, the conventional deflection yoke 4 for use in cathode ray tube has the following shortcomings.
First, in case of the circular deflection yoke, its circular shaped deflection coil creates an unnecessary distance between the electron beams and the deflection coil as illustrated, and as the result thereof, the deflection sensitivity is worse. In FIG. 10, ΔV is a vertical distance between the electron beams and the deflection coil and ΔH is a horizontal distance between the electron beams and the deflection coil. This problem becomes more serious for an wide angle deflection yoke. Hence, it seems almost impossible to develop a high-resolution, high frequency deflection yoke at this point.
Second, a percentage of contraction of the ferrite core 44 mounted in RAC deflection yoke reaches 20%, and the process tolerance due to limitations existing in a manufacturing process is ±2%. In addition, in case of the conventional ferrite core 44, of which inner surface has a rectangular shape (despite the original purpose of using the rectangular shaped inner surface, such as, enhancing the deflection sensitivity) it gives rise to different diameters for the inner surfaces on the upper and lower sides. In consequence, the process tolerance of the manufacturing process was three times (in maximum) greater than that of the conventional circular core, and the production yield of ferrite cores was at most 50% of the conventional circular cores. In fact, since the shape of the inner surface of the rectangular ferrite core is also rectangular, conducting an abrasive blasting process more effectively during the manufacturing process and therefore maintaining precise size can be very difficult. This small quantity, 50% (at best), of rectangular cores only increased the unit price of the core up to 200% of the conventional circular core.